Acetylcellulose (AC)/silica composites were prepared by sol-gel method in an attempt to realize materials with Young's moduli and bending strengths similar to those of cortical bones. Si(OCH3)(4) (TMOS)-AC-H2O-HNO3-tetrahydrofuran-CH3OC2H4OH solutions were allowed to be gelled, where AC/TMOS mole ratios were defined for AC monomers, and the gels were dried at 30-70 degrees C to obtain composites. The composites prepared from solutions of mole ratios of AC/TMOS = 0.5 and 1.0 were composed of micrometer-sized particles rich in silica surrounded by the matrix rich in AC. The composites from solutions of AC/TMOS = 2.0, on the other hand, the interface between the particles and the matrix was much less distinct. All the composite samples showed good machinability, which could be cut into 5 mm x 2 mm x 4.4 mm rectangular specimens by an electric saw without cracking or fracture. The specimens were subjected to three-point bending test, where the degree of plastic deformation and the fracture strain increased, and Young's modulus and bending strength decreased with increasing AC/TMOS ratio in the starting solutions. When the gels were dried at higher temperatures, Young's modulus and strength increased. Young's modulus and bending strength could be varied in the range of 1.8-3.9 GPa and 48-100 MPa, respectively, by varying the AC/TMOS ratio in solutions and the drying temperature. (c) 2005 Springer Science + Business Media, Inc.